Method and apparatus for high efficiency rectification for various loads

ABSTRACT

An apparatus for converting power includes at least one impedance matching network which receives an electrical signal. The apparatus includes at least one AC to DC converter in communication with the impedance matching network. Also disclosed is a method for powering a load and an apparatus for converting power and additional embodiments of an apparatus for converting power.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/679,784, know U.S. Pat. No. 10,454,452), filed Apr. 6, 2015, whichclaims priority to and is a divisional of U.S. patent application Ser.No. 12/951,367, filed Nov. 22, 2010 (now U.S. Pat. No. 9,000,616), whichclaims priority to and is a continuation of U.S. patent application Ser.No. 11/584,983, filed Oct. 23, 2006 (now U.S. Pat. No. 7,868,482), whichclaims priority to and the benefit of U.S. Provisional PatentApplication Ser. No. 60/729,792, filed Oct. 24, 2005; each of which isincorporated herein by reference in its entirety.

BACKGROUND

The present invention is related to a method and apparatus forconverting power. More specifically, the present invention is related toa method and apparatus for converting power with an AC to DC converter.

The prior art has shown that it is possible to provide power to remotedevices using Radio-Frequency (RF) electromagnetic waves. Wireless powertransfer has been described in great detail by W. C. Brown in U.S. Pat.No. 3,114,517, “Microwave Operated Space Vehicles,” incorporated byreference herein, and within numerous other articles by the statedauthor. Wireless power transfer is also used to provide power toRadio-Frequency Identification (RFID) tags. The transmitted RF power iscaptured by an antenna and rectified using a number of disclosedcircuits to provide Direct Current (DC) to a load. U.S. Pat. No.3,434,678, “Microwave to DC Converter,” incorporated by referenceherein, describes an apparatus for converting microwave power to DCusing the bridge rectifying circuit shown in FIG. 1.

More recent patents such as U.S. Pat. No. 6,140,924, “Rectifying AntennaCircuit,” and U.S. Pat. No. 6,615,074, “Apparatus for Energizing aRemote Station and Related Method,” both incorporated by referenceherein, describe RF to DC converters that are implemented using voltagedoubling rectifier configurations as shown in FIG. 2.

The function of these circuits is acceptable when the input power andthe load impedance are constant. However, variations in either the inputpower or load impedance degrade the overall conversion efficiency of thecircuit. The conversion efficiency is defined as the rectified output DCpower divided by the Alternating Current (AC) power input to therectifier. Examples of how changes in the load resistance (or equivalentresistance) and input power affect the conversion efficiency are shownin FIGS. 3 and 4, respectively.

Changes in the rectifier conversion efficiency for varying input powerand output load were described in U.S. Pat. No. 6,212,431, “PowerTransfer Circuit for Implanted Devices,” incorporated by referenceherein, which teaches in Column 1 lines 55-62 that when transferringpower inductively from an external coil to an implanted device that“Unfortunately, neither the load associated with the implant device northe separation distance between the external coil and the implant coilare constants. Each of these parameters are, in practice, variables,that may vary, e.g., from 3-to-15 mm for the separation distance, and 20to 300 ohms for the load. As a result, optimum power transfer betweenthe external device and implant device is rarely achieved. Thus, a lessthan optimum power transfer condition exists . . . ” In this quotation,the separation distance is analogous to changing the input power to theimplanted device. The solution proposed in U.S. Pat. No. 6,212,431 is tovary a matching parameter on the external transmitting coil to optimizethe power transfer from the external transmitting coil to the implantedreceiving coil. The invention disclosed in U.S. Pat. No. 6,212,431implements the solution at the transmitter, which limits the system toone receiver because the transmitter must vary its output based on asingle receiver. Also, U.S. Pat. No. 6,212,431 makes no mention of arectifying circuit and the effect this may have on the method andapparatus presented. Additionally, U.S. Pat. No. 6,212,431 relies oninductive coupling, which allows the impedance of the implanted deviceto be seen by the transmitting coil in a similar manner of reflectingthe impedance on the secondary side of a transformer to the primaryside. The invention described herein does not rely solely on inductiveor near-field power transfer, but rather includes operation in thefar-field where reflecting the receiving load to the transmitting sideis not possible.

Varying load impedances are also examined in U.S. Pat. No. 6,794,951,incorporated by reference herein, which describes a transmitting circuitto ionize gas to create a plasma. The problem presented is that the loadseen by the transmitter changes depending on the status of the plasma inthe chamber. When no plasma is present, the transmitter sees a certainimpedance value. However, when there is plasma present in the chamber, adifferent impedance value is seen by the transmitter. To combat thisissue, U.S. Pat. No. 6,794,951 proposes a dual impedance matchingcircuit, which is controlled via a switch selection system. During thestart mode, the first impedance matching circuit is used to match whenno plasma is present in the chamber. During the run mode, the secondimpedance matching circuit is used to match the system with plasma inthe chamber. The solution presents a way to drive discrete load valueson an RF transmitter. This solution is limited to the transmitting side,must know the discrete impedance values seen during the multiple modesin order to design the impedance matching networks, must have activeswitching to control the matching network, and is designed to give an RFoutput.

SUMMARY

The present invention pertains to an apparatus for converting power. Theapparatus comprises at least one impedance matching network whichreceives an electrical signal. The apparatus comprises a plurality of ACto DC converters in communication with the impedance matching network.

The present invention pertains to a method for powering a load. Themethod comprises the steps of receiving an electrical signal at animpedance matching network. There is the step of converting the signalat a plurality of AC to DC converters in communication with theimpedance matching network. There is the step of providing current tothe load in communication with the plurality of AC to DC converters.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester for harvesting a signalincluding at least one AC to DC converter which provides a conversionefficiency of the signal of at least 50% for a resistive load range thatcovers at least 100 times the minimum value.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester for harvesting a signalincluding at least one AC to DC converter which provides a conversionefficiency of the signal of at least 50% when charging or recharging acharge storage device for an input power range that covers at least 20dB.

The present invention pertains to an apparatus for converting power. Theapparatus comprises means for harvesting a signal including means forconverting AC to DC which provides a conversion efficiency of the signalof at least 50% when charging or recharging a charge storage device foran input power range that covers at least 20 dB.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester for harvesting a signalincluding at least one AC to DC converter which provides a conversionefficiency of the signal of at least 50% for an input power range thatcovers at least 20 dB.

The present invention pertains to an apparatus for converting power. Theapparatus comprises at least two first impedance matching networks whichreceive an electrical signal. The apparatus comprises at least one AC toDC converter in communication with the first impedance matchingnetworks. The apparatus comprises a combiner in electrical communicationwith the first matching networks.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester including at least one AC to DCconverter. The apparatus comprises at least two non-linear elements,wherein the at least two non-linear elements have differentcharacteristics.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester including at least one AC to DCconverter which provides a conversion efficiency of an input signalhaving at least two peaks in efficiency.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester including at least one AC to DCconverter which provides a conversion efficiency of an input signal ofat least 50% for a range from a predetermined distance to ten times thedistance.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester including at least one AC to DCconverter configured to receive a first input power at a first distancewith a first efficiency, wherein the AC to DC converter receives asecond input power at a second distance with a second efficiency. Thefirst distance is greater than the second distance, and the firstefficiency is substantially similar to the second efficiency.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester including at least one AC to DCconverter which provides an input SWR of less than 2.0 for an inputpower range of at least 16 dB.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester including at least one AC to DCconverter which provides an input SWR of less than 2.0 for a resistiveload range that covers at least 40 times a predetermined minimum value.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester including at least one AC to DCconverter wherein the output resistance of the AC to DC converter variesin response to changes in input power or load resistance.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester including at least one AC to DCconverter which provides a conversion efficiency of an input signal ofat least 50% for an input power range that covers at least 20 dB.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an input interface and at least one AC to DCconverter which provides a conversion efficiency of an input signal ofat least 50% for a resistive load range that covers at least 100 times apredetermined minimum value.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an input interface and at least one AC to DCconverter which provides a conversion efficiency of an input signal ofat least 50% when charging or recharging a charge storage device for aninput power range that covers at least 20 dB.

The present invention pertains to an apparatus for converting power. Theapparatus comprises means for harvesting an input signal including meansfor converting AC to DC which provides a conversion efficiency of theinput signal of at least 50% when recharging a charge storage device foran input power range that covers at least 20 dB.

The present invention pertains to an apparatus for converting power. Theapparatus comprises at least two first impedance matching networks whichreceive an electrical signal. The apparatus comprises a combiner inelectrical communication with the first matching networks. The apparatuscomprises at least one AC to DC converter in communication with thefirst impedance matching networks through the combiner.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an input interface and at least one AC to DCconverter. The apparatus comprises at least two non-linear elements,wherein the at least two non-linear elements have differentcharacteristics.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an input interface and at least one AC to DCconverter which provides a conversion efficiency of an input signalhaving at least two peaks in efficiency.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an input interface and at least one AC to DCconverter which provides a conversion efficiency of an input signal ofat least 50% for a range from a predetermined distance to ten times thedistance.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an input interface and at least one AC to DCconverter configured to receive a first input power at a first distancewith a first efficiency, wherein the AC to DC converter receives asecond input power at a second distance with a second efficiency. Thefirst distance is greater than the second distance, and the firstefficiency is substantially similar to the second efficiency.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an input interface and at least one AC to DCconverter which provides an input SWR of less than 2.0 for an inputpower range of over 16 dB.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an input interface and at least one AC to DCconverter which provides an input SWR of less than 2.0 for a resistiveload range that covers at least 40 times a predetermined minimum value.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an input interface and at least one AC to DCconverter wherein the output resistance of the AC to DC converter variesin response to changes in input power or load resistance.

The present invention pertains to an apparatus for converting power. Theapparatus comprising an input interface and at least one AC to DCconverter which provides a conversion efficiency having at least twopeaks in efficiency versus load resistance.

The present invention pertains to an apparatus for converting power. Theapparatus comprising an input interface and at least one AC to DCconverter which provides a conversion efficiency having at least twopeaks in efficiency versus output current.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester including at least one AC to DCconverter which provides a conversion efficiency having at least twopeaks in efficiency versus load resistance.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester including at least one AC to DCconverter which provides a conversion efficiency having at least twopeaks in efficiency versus output current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a prior art bridge rectifiercircuit.

FIG. 2 is a schematic representation of a prior art voltage doublingrectifier.

FIG. 3 is a graph of a prior art rectifier efficiency versus normalizedload resistance where the optimal value is normalized to one.

FIG. 4 is a graph of a prior art rectifier efficiency versus normalizedinput power where the optimal value is normalized to one.

FIG. 5 is a graph of prior art DC to DC converter efficiency withvarious resistive loads.

FIG. 6 is a graph of AC to DC conversion efficiency of the presentinvention with various resistive loads.

FIG. 7 is a schematic representation of a simplified equivalent circuitfor the input of an AC to DC converter.

FIG. 8 is a schematic representation of a simplified equivalent circuitfor the output of an AC to DC converter.

FIG. 9 is a block diagram of the present invention with a fixed load anda variable input power.

FIG. 10 is a block diagram of a fixed load at the optimal value with avariable input power when using passive selector and combiner blocks.

FIG. 11 is a block diagram of the present invention with a variable loadand a fixed input power.

FIG. 12 is a block diagram of one AC to DC converter with two matchingnetworks used for active selection by the selector block.

FIG. 13 is a block diagram of the present invention with a variable loadand a variable input power.

FIG. 14 is a graph of AC to DC efficiency versus normalized loadresistance, load current, or input power for the present invention wherelowest optimal value is normalized to one.

FIG. 15 is a block diagram of the present invention used to charge orrecharge a battery at a near optimal conversion efficiency over a widerange of input power levels.

FIG. 16 is a block diagram of the present invention with voltageonitoring circuitry after the combiner.

FIG. 17 is a graph of RF to DC conversion efficiency of the presentinvention compared to the prior art.

FIG. 18 is a block diagram of multiple paths for conversion.

FIG. 19 is a block diagram of a single diode, full waved rectifier usewith the present invention.

FIG. 20 is a block diagram of a single diode, halfwave rectifier usedwith the present invention.

FIG. 21 is a block diagram of an embodiment of the apparatus of thepresent invention that was fabricated on a printed circuit board.

FIG. 22 is a graph of measured input SWR data for the embodiment of theinvention shown in FIG. 21 for different input power levels at 905.8MHz.

FIG. 23 is a graph of measured input impedance for the embodiment of theinvention shown in FIG. 21 for different input power levels at 905.8MHz.

FIG. 24 is a graph of measured input impedance for the embodiment of theinvention shown in FIG. 21 for different input power levels at 905.8 MHzwherein impedances within the Smith chart circle correspond to SWRvalues of less than 2.0.

FIG. 25 is another embodiment of the present invention.

DETAILED DESCRIPTION

A complete understanding of the invention will be obtained from thefollowing description when taken in connection with the accompanyingdrawing figures wherein like reference characters identify like partsthroughout.

For purposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the invention as it is oriented inthe drawing figures. However, it is to be understood that the inventionmay assume various alternative variations and step sequences, exceptwhere expressly specified to the contrary. It is also to be understoodthat the specific devices and processes illustrated in the attacheddrawings, and described in the following specification, are simplyexemplary embodiments of the invention. Hence, specific dimensions andother physical characteristics related to the embodiments disclosedherein are not to be considered as limiting.

Referring now to the drawings wherein like reference numerals refer tosimilar or identical parts throughout the several views, and morespecifically to FIG. 9 thereof, there is shown an apparatus 10 forconverting power. The apparatus 10 comprises at least one firstimpedance matching network 12 which receives an electrical signal. Theapparatus 10 comprises a plurality of AC to DC converters 14 incommunication with the first impedance matching network 12 andconfigured to be communicable with a load 16, wherein the apparatus 10is configured to be communicable with an input.

Preferably, there is a plurality of first impedance matching networks 12in communication with the plurality of the AC to DC converters 14. Theapparatus 10 preferably includes a selector 18 for directing the signalto the first impedance matching networks 12. Preferably, the selector 18is active or passive.

The apparatus 10 preferably includes a combiner 20 connected to theplurality of AC to DC converters 14 for combining outputs of the AC toDC converters 14. Preferably, the combiner 20 is active or passive. Theplurality of AC to DC converters 14 preferably define a plurality of ACto DC paths 22, where each path is optimized for a given characteristic.The apparatus 10 can include a second impedance matching network 24 thatis configured to match an impedance of the apparatus 10 with animpedance of the input. Preferably, each AC to DC path 22 is matched toa predetermined impedance value. Each AC to DC path 22 preferably has adifferent output resistance. Each AC to DC converter 14 input can bematched to a predetermined impedance value at different input powerlevels using the at least one first impedance matching network 12.

In an embodiment when the selector 18 is active, there can be a selectorcontrol unit 26 that selects the appropriate AC to DC converter 14 basedon input power level or load 16 resistance. There can be a combiner 20connected to the plurality of AC to DC converters 14 and for combiningoutputs of the AC to DC converters 14, wherein the combiner 20 is activeand including a combiner control unit 30. The selector 18 control unitand the combiner 20 control unit can be the same control unit.

In another embodiment, one of the AC to DC converters' 14 outputresistance is designed to be at or near one discrete resistance that theload 16 is at or near for some time; and another of the AC to DCconverters' 14 output resistance is designed to be at or near adifferent discrete resistance that the load 16 is at or near for someother time.

Each of the AC to DC converters 14 can have a different outputresistance corresponding to an associated optimal load 16. One of the ACto DC converters' 14 input impedance can be matched to a predeterminedvalue at one power level, and another of the AC to DC converters' 14input impedance is matched to another predetermined value at a differentpower level.

The load can be a battery 32 to which each AC to DC converter 14 is inelectrical communication with and each AC to DC path 22 is optimized fora specific input power level and load 16 resistance, as shown in FIG.15. There can be a voltage monitoring circuit 34 connected between theplurality of AC to DC converters 14 and the battery 32 and insures thata voltage level stays within a specified range, as shown in FIG. 16.There can be a printed circuit board 36 on which the plurality of AC toDC converters 14 and the at least one first matching network aredisposed.

In yet another embodiment, the apparatus 10 is included in an energyharvester 38 that produces the electrical signal. The energy harvester38 can include an antenna 48, a piezoelectric element 50, a solar cell,a generator, a vibration harvester, an acoustic harvester or a windharvester, as shown in FIG. 25. At least one of the plurality of AC toDC converters 14 can be either a single diode full wave rectifier 40 ora single diode half wave rectifier 42, as shown in FIGS. 19 and 20,respectively. At least one of the plurality of AC to DC converters 14can be a voltage doubler.

The load 16 can include at least one power storage element 44 inelectrical communication with at least one of the AC to DC converters14. The load 16 can be fixed at or near the load's 16 optimalresistance, and the electrical signal provides an input power that isvariable, as shown in FIG. 10. The load 16 can be variable and theelectrical signal provides an input power that is fixed, as shown inFIG. 11. Alternatively, the load 16 is variable and the electricalsignal provides an input power that is variable, as shown in FIG. 13.The load 16 can be an LED.

The present invention pertains to a method for powering a load 16. Themethod comprises the steps of receiving an electrical signal at animpedance matching network. There is the step of converting the signalat a plurality of AC to DC converters 14 in communication with theimpedance matching network. There is the step of providing current tothe load 16 in communication with the plurality of AC to DC converters14.

Preferably, the receiving step includes the step of receiving theelectrical signal at a plurality of impedance matching networks incommunication with the plurality of the AC to DC converters 14. There ispreferably the step of directing the signal with a selector 18.Preferably, the selector 18 is active or passive.

There can be the step of combining outputs from the plurality of AC toDC converters 14 with a combiner 20 connected to the load 16.Preferably, the combiner 20 is active or passive.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an energy harvester 38 including at least oneAC to DC converter 14 which provides a conversion efficiency of an inputsignal of at least 50% for an input power range that covers at least 20dB.

Preferably, the AC to DC converter 14 is used in an energy harvester 38.The energy harvester 38 can include an antenna 48. Alternatively, theenergy harvester 38 can include a piezoelectric element 50.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an energy harvester 38 including at least oneAC to DC converter 14 which provides a conversion efficiency of an inputsignal of at least 50% for a resistive load 16 range that covers atleast 100 times a predetermined minimum value.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an energy harvester 38 including at least oneAC to DC converter 14 which provides a conversion efficiency of an inputsignal of at least 50% when recharging a charge storage device for aninput power range that covers at least 20 dB.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises means for harvesting an input signalincluding means for converting AC to DC which provides a conversionefficiency of the input signal of at least 50% when recharging a chargestorage device for an input power range that covers at least 20 dB. Themeans for converting AC to DC can be an AC to DC converter 14. The meansfor harvesting a signal can be an energy harvester 38.

The present invention pertains to an apparatus 10 for converting power,as shown in FIG. 12. The apparatus 10 comprises at least two firstimpedance matching networks 12 which receive an electrical signal. Theapparatus 10 comprises a combiner 20 in electrical communication withthe first matching networks. The apparatus 10 comprises at least one ACto DC converter 14 in communication with the first impedance matchingnetworks 12 through the combiner 20. Preferably, the combiner 20 is aswitch.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an energy harvester 38 including at least oneAC to DC converter 14. The apparatus 10 comprises at least twonon-linear elements, wherein the at least two non-linear elements havedifferent characteristics.

Preferably, the at least two non-linear elements are one or more ofdiodes, mosfets, or transistors. The different characteristicspreferably include different impedances or different resistances.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an energy harvester 38 including at least oneAC to DC converter 14 which provides a conversion efficiency of an inputsignal having at least two peaks in efficiency.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an energy harvester 38 including at least oneAC to DC converter 14 which provides a conversion efficiency of an inputsignal of at least 50% for a range from a predetermined distance to tentimes the distance.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an energy harvester 38 including at least oneAC to DC converter 14 configured to receive a first input power at afirst distance with a first efficiency, wherein the AC to DC converter14 receives a second input power at a second distance with a secondefficiency. The first distance is greater than the second distance, andthe first efficiency is substantially similar to the second efficiency.

Preferably, the first input power and the second input power are formedby pulses of power.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an energy harvester 38 including at least oneAC to DC converter 14 which provides an input SWR of less than 2.0 foran input power range of at least 16 dB.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an energy harvester 38 including at least oneAC to DC converter 14 which provides an input SWR of less than 2.0 for aresistive load 16 range that covers at least 40 times a predeterminedminimum value.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an energy harvester 38 including at least oneAC to DC converter 14 wherein the output resistance of the AC to DCconverter 14 varies in response to changes in input power or load 16resistance.

The apparatus 10 preferably includes a voltage monitoring circuit 34that insures that a voltage level stays within a specified range.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an energy harvester 38 including at least oneAC to DC converter 14 which provides a conversion efficiency of an inputsignal of at least 50% for an input power range that covers at least 20dB.

Preferably, the AC to DC converter 14 is used in an energy harvester 38.The energy harvester 38 can include an antenna 48. Alternatively, theenergy harvester 38 can include a piezoelectric element 50.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an input interface and at least one AC to DCconverter 14 which provides a conversion efficiency of an input signalof at least 50% for a resistive load 16 range that covers at least 100times a predetermined minimum value. An input interface may be aconnector, wire, pin, lead, or any other suitable element that canaccept the input signal.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an input interface and at least one AC to DCconverter 14 which provides a conversion efficiency of an input signalof at least 50% when recharging a charge storage device for an inputpower range that covers at least 20 dB.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises means for harvesting an input signalincluding means for converting AC to DC which provides a conversionefficiency of the input signal of at least 50% when recharging a chargestorage device for an input power range that covers at least 20 dB.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises at least two first impedance matchingnetworks 12 which receive an electrical signal. The apparatus 10comprises at least one AC to DC converter 14 in communication with thefirst impedance matching networks 12. The apparatus 10 comprises acombiner 20 in electrical communication with the first matchingnetworks. Preferably, the combiner 20 is a switch.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an input interface and at least one AC to DCconverter 14. The apparatus 10 comprises at least two non-linearelements, wherein the at least two non-linear elements have differentcharacteristics. Preferably, the at least two non-linear elements areone or more of diodes, mosfets, or transistors. The differentcharacteristics preferably include different impedances or differentresistances.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an input interface and at least one AC to DCconverter 14 which provides a conversion efficiency of an input signalhaving at least two peaks in efficiency.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an input interface and at least one AC to DCconverter 14 which provides a conversion efficiency of an input signalof at least 50% for a range from a predetermined distance to ten timesthe distance.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an input interface and at least one AC to DCconverter 14 configured to receive a first input power at a firstdistance with a first efficiency, wherein the AC to DC converter 14receives a second input power at a second distance with a secondefficiency. The first distance is greater than the second distance, andthe first efficiency is substantially similar to the second efficiency.Preferably, the first input power and the second input power are formedby pulses of power.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an input interface and at least one AC to DCconverter 14 which provides an input SWR of less than 2.0 for an inputpower range of at least 16 dB.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an input interface and at least one AC to DCconverter 14 which provides an input SWR of less than 2.0 for aresistive load 16 range that covers at least 40 times a predeterminedminimum value.

The present invention pertains to an apparatus 10 for converting power.The apparatus 10 comprises an input interface and at least one AC to DCconverter 14 wherein the output resistance of the AC to DC converter 14varies in response to changes in input power or load 16 resistance. Theapparatus 10 preferably includes a voltage monitoring circuit 34 thatinsures that a voltage level stays within a specified range.

The present invention pertains to an apparatus for converting power. Theapparatus comprising an input interface and at least one AC to DCconverter which provides a conversion efficiency having at least twopeaks in efficiency versus load resistance.

The present invention pertains to an apparatus for converting power. Theapparatus comprising an input interface and at least one AC to DCconverter which provides a conversion efficiency having at least twopeaks in efficiency versus output current.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester including at least one AC to DCconverter which provides a conversion efficiency having at least twopeaks in efficiency versus load resistance.

The present invention pertains to an apparatus for converting power. Theapparatus comprises an energy harvester including at least one AC to DCconverter which provides a conversion efficiency having at least twopeaks in efficiency versus output current.

The present invention discloses a method and apparatus 10 that providesa far superior solution for efficiently converting AC to DC for varyingloads and input power levels than the prior art. Efficient conversionfrom AC to DC in this case is defined as being greater than fifty (50)percent; however, different applications may have different definitions.The invention can be applied not only to the inductive (near field) butalso to the far field region. The far field region is commonly definedas

$r \geq \frac{2D^{2}}{\lambda}$where r is the distance between the transmitting and receiving antennas48, D is the maximum dimension of either the transmitting or receivingantenna 48, and lambda is the wavelength. The invention is implementedin the AC to DC circuitry to allow multiple devices to operate from asingle power transmitter unlike the referenced prior art, whichimplements solutions on the transmitting side.

When examining the prior art, the circuit shown in FIG. 2 when designedproperly is able to drive a fixed resistive load 16 over a limited inputpower range with minimal effect on the equivalent impedance of the AC toDC converter 14 and load 16. However, when the load 16 is changed theconversion efficiency is reduced. Significant reductions are consideredthose that reduce the efficiency by 2 or more percent and/or reduce theAC to DC conversion efficiency below the application specific thresholdsuch as fifty percent conversion efficiency. As an example, the circuitin FIG. 2 was constructed with a potentiometer as the load 16. The inputwas matched to 50-ohms and was connected to an RF network analyzer. TheAC to DC conversion efficiency was then measured for various input powerlevels for a potentiometer setting of 10 k-ohm, 5 k-ohm, 2.5 k-ohm, and1.25 k-ohm. The results seen in FIG. 5 show that a change from theoptimal load 16 of 10 k-ohm to 5 k-ohm reduces the AC to DC conversionefficiency at 0 dBm (dBm is decibels referenced to 1 milli-watt) from66.25 percent to 59.58 percent, respectively. The reduction is fargreater for a change from 10 k-ohm to 2.5 k-ohm, which reduces the AC toDC conversion efficiency at 0 dBm from 66.25 percent to 43.18 percent,respectively. The reduction is even more dramatic for a change from 10k-ohm to 1.25 k-ohm, which reduces the AC to DC conversion efficiency at0 dBm from 66.25 percent to 26.91 percent, respectively.

The invention described herein, however, does not have an AC to DCconversion efficiency that is as significantly affected by the load 16resistance as the prior art shown in FIG. 5. To illustrate this, theinvention was also measured with a potentiometer as the load 16 withsettings of 10 k-ohm, 5 k-ohm, 2.5 k-ohm, and 1.25 k-ohm. The resultsare shown in FIG. 6, which illustrates that a change from the optimalload 16 of 10 k-ohm to 5 k-ohm reduces the AC to DC conversionefficiency at 0 dBm from 61.75 percent to only 54.19 percent,respectively. The change from 10 k-ohm to 2.5 k-ohm reduces the AC to DCconversion efficiency at 0 dBm from 61.75 percent to 54.94 percent,respectively. The change from 10 k-ohm to 1.25 k-ohm reduces the AC toDC conversion efficiency at 0 dBm from 61.75 percent to 48.42 percent,respectively. As can be seen, the invention has a slightly lower AC toDC conversion efficiency at the optimal load 16 resistance at 0 dBm,however, the AC to DC conversion efficiencies at other loads 16 remainhigher than the prior art specifically at the lowest value of the load16 resistance, 1.25 k-ohm. The invention also significantly outperformsthe prior art at power levels above 0 dBm.

The reduction in conversion efficiency shown in FIG. 5 is magnified whena battery 32 or other power storage element 44 such as a large capacitoror LED is connected to the AC to DC converter 14 for the purpose ofrecharging or powering. The battery 32, power storage element 44, or LEDholds a fairly constant voltage and therefore changes in input powerpower result in changes in the output current, which changes theequivalent resistance seen at the output of the AC to DC converter 14.The equivalent resistance is defined as the output voltage divided bythe output current. As an example, if one milliwatt (1 mW) is input toan AC to DC converter 14 connected to a 3-volt battery 32 and the AC toDC conversion efficiency is 50 percent, the equivalent load 16 seen bythe AC to DC converter 14 is given by

$R_{EQ} = {\frac{V_{B}}{I_{B}} = {\frac{V_{B}^{2}}{{eP}_{IN}} = \frac{V_{B}^{2}}{P_{OUT}}}}$where V_(B) is the battery 32 voltage, 1 _(B) is the current through thebattery 32, e is the AC to DC conversion efficiency, P_(IN) is the inputpower to the AC to DC converter 14, and P_(OUT) is the output power fromthe AC to DC converter 14. For this example, the equivalent resistanceis 18 k-ohm. However, if the input power is changed to two milliwatts (2mW) and the conversion efficiency remains 50 percent the equivalentresistance is reduced to 9 k-ohm. Using this example, it can be seenthat the equivalent load 16 resistance is inversely proportional to theinput power to the AC to DC converter 14.

The changes in conversion efficiency for AC to DC converters 14 can bebroken into two categories. First, power can be lost (reflected) whenthe equivalent impedance of the AC to DC converter 14 and load 16,Z_(EQ), is not the complex conjugate of the source impedance. An exampleis shown in FIG. 7. This loss can be seen by examining the Maximum PowerTransfer Theorem, which is well known to those skilled in the art. TheMaximum Power Transfer Theorem states that the maximum power istransferred from the source to the load 16 when the source and load 16impedance are complex conjugates.

The second form of efficiency loss is caused by mismatch between the DCoutput resistance of the AC to DC converter 14 and the load 16resistance. For the purpose of this invention, impedance mismatch isconsidered significant if more than ten percent of the power isreflected or lost. For the AC to DC converter 14, the output is DC andtherefore the resistances must be equal. A simplified equivalent circuitfor the output of an AC to DC converter 14 can be seen in FIG. 8 whereR_(O) is the DC output resistance of the AC to DC converter 14 and R_(L)is the load 16 resistance. From FIG. 8 and the Maximum Power TransferTheorem, the maximum power will be delivered from the AC to DC converter14 to the load 16 when R_(O)=R_(L). This condition will therefore betermed the optimal load 16 resistance. It should be noted that the twoefficiency losses are linked together. As an example, varying the load16 resistor not only causes loss due to DC output mismatch, but thechange in load 16 resistance also changes the equivalent impedance seenby the source, which causes input mismatch.

The present invention addresses the two efficiency losses previouslystated by creating multiple AC to DC paths 22 by use of multiple AC toDC converters 14. The multiple paths allow each path to be optimized fora given characteristic to provide a near optimal performance over awider range of input parameters.

The present invention can be implemented for a number of differentcombinations. In a first embodiment, the load 16 is fixed at or near theoptimal load 16 resistance, which was described above, and the inputpower is variable. As stated previously, with proper design the AC to DCconverter 14 in FIG. 2 can efficiently drive a fixed load 16 over alimited input power range. This can be seen in FIG. 5. However, if it isdesired to efficiently drive the load 16 over a larger input power rangethan can be provided by the prior art or if it is found to beadvantageous in other applications where the load 16 is fixed, theinvention can be used. A block diagram of an embodiment of the inventioncan be seen in FIG. 9, where the AC to DC converter includes a selector,two first impedance matching networks 12, two AC to DC converters 14,and a combiner 20 in communication with an input and a load 16.

As shown in FIG. 9, the input is an AC source with a source impedance,R_(S), which are initially matched to the equivalent circuit of theselector 18, the AC to DC converters 14 and their associated firstimpedance matching networks 12, the combiner 20, and the load 16 usingthe second impedance matching network 24. The first and second impedancematching networks 12, 24 can be, but are not limited to, Pi-, T-, L-,single series element, or single shunt element network that can containcombinations of inductors and capacitors well known to those skilled inthe art and described in detail in the books, “Antenna ImpedanceMatching” by the author Wilfred N. Caron and “The Design ofImpedance-Matching Networks for Radio-Frequency and MicrowaveAmplifiers” by the author Pieter L. D. Abrie, both incorporated byreference herein. It should be noted that the capacitors and inductorsused in the first and second impedance matching networks 12, 24 may bediscrete elements, elements formed on a substrate such as a Printedcircuit board 36 (PCB) or chip, intrinsic elements, or parasiticelements. The output from the second impedance matching network 24 isconnected to the selector 18, which directs the signal to theappropriate AC to DC path 22. The selector 18 can be, but is not limitedto, a simple hardwired connection, such as a microstrip line, abalanced-unbalanced (balun) transformer, or an active switching circuitsuch as a transistor, pin diode(s), or relay. Each AC to DC path 22 ismatched to a predetermined impedance value, such as 50 ohms for standardantenna types, at different power levels using their respective firstimpedance matching networks 12 and impedance matching techniques knownto those skilled in the art. The output from each AC to DC converter 14is then combined using the combiner 20, and the combined DC is sent tothe load 16. The combiner 20 can be, but is not limited to, a simplehardwired connection such as a microstrip line, discrete components suchas diodes, or an active switching circuit such as a transistor, pindiode(s), or relay. The second impedance matching network 24 next to theinput may be needed if the two paths interfere with each other, whichmay be the case if using a passive selector 18 and/or combiner 20 thatcan be implemented with a directly wired connection. The AC to DCconverters 14 that can be used with the invention can be, but are notlimited to, a voltage doubler (one or more stages), charge pump, peakdetector (series or shunt), bridge rectifier, or other AC rectifyingcircuits.

It has been determined through experimentation that the circuit shown inFIG. 2 can efficiently drive the fixed optimal load 16 resistance over arange of −7 to +10 dBm (17 dB range, see FIG. 5) when matched at 0 dBmand designed properly. However, if a range of −20 to +10 dBm isrequired, the circuit in FIG. 2 will suffer from the effects shown inFIG. 4, and the conversion efficiency will be reduced below 50 percentat the lower power level (less than −7 dBm). The reduction in theconversion efficiency for this case is caused by power reflected at theinput to the AC to DC converter 14 in FIG. 2 due to an impedancemismatch. The impedance mismatch is caused by the change in the inputpower. The AC to DC converter 14 contains nonlinear elements. Thenonlinear nature of the elements means their impedance values changewith the power level, which will in turn cause an impedance mismatchbetween the source and the AC to DC converter 14.

A solution to this problem is to use the AC to DC converter 14 in FIG. 9where the top AC to DC converter 14 is matched at −13 dBm and the bottomAC to DC converter 14 is matched at +0 dBm. The selector 18 can thenchoose the appropriate path for the input signal depending on the inputpower level. The top AC to DC converter 14 will be able to drive thefixed optimal load 16 resistance over a 17 dB range as previouslystated, meaning it can convert the input AC signal efficiently over the−20 dBm to −3 dBm range. The bottom AC to DC converter 14 can alsoefficiently convert the input AC signal over a 17 dB range, which meansit can convert input signals with power levels from −7 dBm to +10 dBm.The combination of the two AC to DC converters 14 allows the entire ACto DC converting system to accept input power levels from −20 dBm to +10dBm or a 30 dB power range which is 20 times the range of a single AC toDC converter 14.

It should be noted that the selector 18 may be either active or passive.In the active case, a control unit is used to select the appropriatepath for the incoming signal based on the power level or load 16resistance. If the selector 18 is a passive unit, it can be implementedby, but not limited to, a simple wired connection. In this case, thesignal would be supplied to the inputs of both AC to DC converter's 14first impedance matching networks 12. The signal would split itself withmost power choosing the path with the least mismatch at the power levelof the input signal.

The combiner 20 may take many different forms depending on theconfiguration of the rest of the system. As an example, the combiner 20,if active, may be implemented with a switch similar to the one used inthe selector 18, if active, and both could be controlled by the samecontroller or a different controller. In the active case, a control unitis used to select the appropriate path for the incoming signal based onthe power level or load 16 resistance. When a passive system isadvantageous, the combiner 20 can be implemented with a simple wiredconnection as long as the output of the unused AC to DC path 22 will notaffect the performance or with one or more blocking diodes. An exampleconverter for the passive case for both the selector 18 and combiner 20is shown in FIG. 10 where the matching has been configured to match theprevious example.

A second embodiment for how the invention can be implemented is to havea fixed input power and a variable load 16 resistance, which is shown inFIG. 11.

In the prior art circuit in FIG. 2, there will be loss described by theMaximum Power Transfer Theorem due to the mismatch of the AC to DCconverter 14 output resistance and the load 16 resistance. Thecorresponding conversion efficiency will be similar to that shown inFIG. 3. The AC to DC converter 14 in FIG. 2 can be matched to loads 16other than the optimal load 16 resistance to minimize the loss inconversion efficiency caused by input mismatch at that load 16resistance value. However, there will still be loss in conversionefficiency due to the mismatch between the AC to DC converter 14 outputDC resistance and the load 16 resistance and the conversion efficiencywill take a shape similar to that shown in FIG. 3. There will also beloss due to impedance mismatch between the impedance of the input andthe input of the AC to DC converter 14 caused by the change in the load16 resistance.

The invention can be used to combat the issue of reduced conversionefficiency by matching the top AC to DC converter 14 in FIG. 11 at ornear one discrete resistance that the variable load 16 is at or near forsome time. The bottom AC to DC converter 14 in FIG. 11 is matched to adifferent discrete resistance that the variable load 16 is at or nearfor some time. This technique will reduce the loss caused by impedancemismatch between the impedance of the input and the input of the AC toDC converter 14 caused by the change in the load 16 resistance as wasshown in FIG. 5. However, the loss caused by the mismatch between the ACto DC converter 14 output DC resistance and the load 16 resistance isstill present in this case.

In the two previous embodiments, fixed input power/variable load 16resistance and fixed load 16 resistance/variable input power, anobservation can be made; multiple AC to DC converter 14 paths may not beneeded if the combiner 20 is put before the AC to DC converter 14 asshown in FIG. 12. This would essentially be switching between the twofirst impedance matching networks 12 to work with the same AC to DCconverter 14. This realization is valid when the selection by theselector 18 and combiner 20 is done with an active element such as atransistor, pin diode, or relay, which would be controlled by acontroller. If passive selection is used by a simple wired connection,the realization of using a single AC to DC converter 14 is no longervalid due to the fact that the parallel matching networks will reduce toa single matching network yielding the same problems present in theprior art.

For the passive selection case, an AC to DC converter 14 on each pathinsures that the AC signal is not present at the output. The lack of ACat the output means the two path outputs will not destructivelyinterfere. The lack of AC at the output is sometimes referred to asdestroying the phase. It should be noted that for the active selectioncase, it may be found advantageous to still include both AC to DCconverters 14. However, the AC to DC converters 14 can be reduced to asingle AC to DC converter 14 for most applications.

A third and more practical embodiment of how the invention can beimplemented is for a variable input power and a variable load 16resistance, which is shown in FIG. 13.

A realistic situation in AC to DC converting applications, such as RF toDC conversion, is to have a variable input power and a variable load 16resistance. This situation combines the problems associated with theprevious two embodiments (fixed input power/variable load 16 resistanceand fixed load 16 resistance/variable input power). These problems arelosses caused by input and output impedance mismatch of the AC to DCconverter 14. The solution for the input impedance mismatch waspresented in the first embodiment, which matched each path at adifferent power level for the optimal load 16 resistance. The problemwith this embodiment is that it was limited to the optimal load 16resistance. The remaining problem in the first embodiment was the losscaused for non-optimal loads 16 by the resistive mismatch between theoutput resistance of the AC to DC converter 14 and the resistive load16. This problem was addressed in the second embodiment by matching eachpath to a different resistance. The issue with the second embodiment wasthat it was for a fixed power and power level changes would causemismatch at the input to the AC to DC converter 14 thus causing theconversion efficiency to be reduced.

A solution to the output mismatch loss and the input mismatch loss is toadjust the parameters of the AC to DC converters 14 so they havedifferent output resistance thus enabling the converter to have morethan one optimal load 16. In other words, the output resistance varieswith input power and/or load 16 resistance. The parameters may beadjusted by using different diodes, transistors, or other non-linearelements or by using different AC to DC topologies. Preferably,different diodes are used wherein at least one diode has a differentresistance, impedance, turn-on voltage, junction capacitance, or othercharacteristic. This technique can then be implemented in conjunctionwith the method described in the first embodiment, which matched eachpath at a different power level. The result provides an AC to DCconversion efficiency graph with two peaks unlike the single peak shownin FIG. 3. The resulting graph has a nearly constant conversionefficiency over a wider range of load 16 resistances as shown in FIG.14.

The technique of multiple AC to DC paths 22 matched at different inputpower levels with different output resistances works exceptionally wellwhen connecting the converter to a battery 32 for recharging purposes orto an LED for direct powering. The battery 32 or LED equivalentresistance is inversely proportional to the input power to the AC to DCconverter 14, which means at low power levels the battery 32 or LEDlooks like a large resistor while at high power levels the battery 32 orLED looks like a small resistor. This realization allows each path to beoptimized for a specific power level and load 16 resistance. As anexample, the upper AC to DC path 22 in FIG. 13 could be impedancematched at a high power level and the AC to DC converter 14 in that pathcould be designed to have a low optimal load 16 resistance. The lowerpath, on the other hand, could be impedance matched at a low power leveland the AC to DC converter 14 in that path could be designed to have ahigh optimal load 16 resistance. The resulting converter using passiveselector 18 and combiner 20 (directly wired) can be seen in FIG. 15.

It should be noted that for battery 32 (or for other storage) chargingand applications where circuits or resistive loads are driven directly,it may be necessary to place a voltage monitoring circuit 34 on theoutput of the combiner 20 to ensure that the voltage level stays withina specified range. The voltage monitoring circuit 34 can include, but isnot limited to, over-voltage protection, under-voltage protection, orsome combination of the two; regulator; DC to DC converter; or any othercircuit that can ensure that the voltage level stays within a specifiedrange. This can be seen in FIG. 16.

The concepts described herein have been verified in an RF powerharvesting application. The converter shown in FIG. 21 was fabricated ona Printed circuit board 36 (PCB), although it is possible to form theconverter on a semiconductor or equivalent chip. In the fabricatedconverter, the AC source and source resistance in the Figure have beenimplemented with an energy harvesting antenna 48 and the matching andoutput resistances were designed to drive a 3-volt battery 32. Theresults of tests showed that the design had a conversion efficiency ofover 50 percent over a range from −1 dBm to +20 dBm, which can be seenin FIG. 17 and is compared to the prior art, while maintaining aStanding Wave Ratio (SWR) of under 2.0 over almost the entire range fora frequency of 905.8 Mega-Hertz (MHz) and a 3-volt battery 32. The SWRis a measurement that describes how well the equivalent circuit of theAC to DC converter 14 and load 16 resistance is matched to the impedanceof the input, which in this case was a 50-ohm antenna 48. FIGS. 22-24show the SWR data measured using a network analyzer. As is shown in theFigs., the AC to DC converter had an SWR of less than 2.0 for an inputpower of −1.82 dBm to 14.3 dBm or a range of over 16 dB. The same istrue for a load 16 range of over 16 dB (range covering 40 times aminimum value), that is, the SWR is less than 2.0. An SWR value of 2.0is approximately a reflection loss of 10 percent.

It is important to note that in RF power harvesting applications, thepower range of the converter, −1 dBm to +20 dBm for this example, can betranslated into distance from a powering transmitter. It is well knownto those skilled in the art that the power available at a receivingantenna 48 in the far-field is inversely proportional to the square ofthe distance between the transmitter and receiver. Given this fact andthe −1 dBm to +20 dBm power range (where the difference from the lowestpower to the highest power is approximately 20 dB or 100 times thelowest power), the distance in which the conversion efficiency is over50% for this example will be from a distance X to a distanceproportional to the square root of the power range, or for this case thesquare root of 100. Using this example it can be seen that thefabricated converter can convert greater than 50% of the available powerfrom a distance X to a greater distance of 10X where X is determined bythe power setting, gain, and algorithm of the powering transmitter. Inother words, the conversion efficiency of the invention does notsubstantially change for changes in distance. It should be noted thatthe AC to DC conversion efficiency of the invention at a given time isbased on the instantaneous power level (power level at that given time)and, therefore, using a transmitter algorithm such as a pulsingalgorithm, as disclosed in U.S. Provisional application 60/656,165, andrelated U.S. patent application Ser. No. 11/356,892, incorporated byreference herein, the invention is able to efficiently convert AC to DCat much lower average input power levels than those depicted in FIG. 17.As an example, if a 0 dBm continuous wave (CW) AC input is supplied tothe invention, from FIG. 17, the conversion efficiency will beapproximately 57 percent because the peak instantaneous power is 0 dBm.However, if 0 dBm is pulsed at a 25 percent duty cycle, the averagepower is a fourth of 0 dBm or −6 dBm. According to FIG. 17, theconversion efficiency at −6 dBm is zero percent. However, the use ofpulsing means the input power has a peak instantaneous power of 0 dBmduring the pulse and therefore the AC to DC conversion efficiency isstill approximately 57 percent. As this example shows, the use ofpulsing allows the AC to DC conversion efficiency graph in FIG. 17 to beshifted to the lower power levels by adjusting the peak power levels ofthe pulses to fall within the high efficiency conversion region whichfor FIG. 17 is −1 to 20 dBm. The average power, however, may be outsidethe high efficiency conversion region. In RF power harvestingapplications, using the pulsing method with the invention allows the ACto DC converter 14 to efficiently convert the RF energy captured by theantenna 48 for the same average power as a CW signal at a much greaterdistance from the transmitter.

Since light is a form of AC, the technique described herein can also beapplied to solar panels and other light to DC converting circuits. Theconcepts described are still applicable; however, the blocks may not berepresented by electrical circuits but rather optical devices such as,but limited to, lens, optical filters, optical fiber, etc. An examplefor how a solar panel could use the concepts described in the inventioncan be developed by realization that a solar cell suffers from the sameconversion efficiency as described by FIG. 3. There is an optimal valueof the solar cell load 16 resistor that produces the maximum outputpower. The technique described herein could be applied by creatingadjacent solar cells with different output resistance to enable thesolar panel to have more than one optimal resistive load 16 which allowsthe solar panel to have a near optimal conversion efficiency across awider range of load 16 resistances.

As shown with the solar cell example, the invention can be applied toany number of fields such as, but not limited to, rectifying circuitsfor converting AC to DC in RF power harvesting, piezoelectric powerharvesting, solar cells, generators, vibration harvesting, acousticharvesting, or any other application requiring conversion of AC to DC.As the previous list of applications shows, the invention has numerousimplementations in the energy harvesting or power harvesting field.Energy harvesting is defined as capturing energy from the surroundingsand converting the captured energy into another form of energy. Capturedenergy may be specifically created for the purpose of harvesting or beambient, meaning the energy is from the environment or created foranother purpose such as, but not limited to, sunlight and radiocommunications, respectively. The apparatus 10 that harvests the energyis termed the energy harvester 38 and may include, but is not limitedto, an antenna 48, a piezoelectric element 50, a solar cell, agenerator, a vibration harvester, an acoustic harvester, a windharvester, any other element or elements that harvest energy, an AC toDC converter 14, a voltage doubler (one or more stages), charge pump,peak detector (series or shunt), bridge rectifier, other AC rectifyingcircuits, or the invention.

It should be noted that the embodiments outlined above could be appliedto other storage devices such as, but not limited to, a capacitor. Theconverter could also be designed to directly drive any circuit that runsin more than one mode of operation, such as, but not limited to, amicrocontroller that runs in sleep mode and active mode. The equivalentresistance of the microcontroller would be high in sleep mode and low inactive mode, giving the need for efficient conversion of AC to DC overmore than one resistive load 16.

There may be a need for the converter to have an even wider range ofinput power levels and/or load 16 resistances. For this circumstance,more than two AC to DC paths 22 could be implemented using the sameprocedure described in detail herein. An example of this is shown inFIG. 18, where a plurality of AC to DC paths 22 is illustrated.

The invention is designed to be independent of the type of AC to DCconverters 14 that can be used. Several AC to DC converters 14 weretested and are known to work with the invention. FIG. 2 shows a voltagedoubler from the prior art, which has been tested with the invention.FIG. 19 shows a single diode, full wave rectifier 40 that has beentested and is known to work with the invention. It should be noted thatdifferent AC to DC converter 14 topologies, as shown in FIGS. 2, 19, and20, may be used within the invention to produce a desired effect.

FIG. 20 shows a single diode, half wave rectifier 42 that has beentested and is known to work with the invention. The invention will workwith any other AC rectifying circuits.

FIG. 22 is a graph of measured input SWR data for the embodiment of theinvention shown in FIG. 21 for different input power levels at 905.8MHz.

FIG. 23 is a graph of measured input impedance for the embodiment of theinvention shown in FIG. 21 for different input power levels at 905.8MHz.

FIG. 24 is a graph of measured input impedance for the embodiment of theinvention shown in FIG. 21 for different input power levels at 905.8 MHzwherein impedances within the Smith chart circle correspond to SWRvalues of less than 2.0.

FIG. 13 is a block diagram of the present invention with a variable loadand a variable input power. The apparatus shown in FIG. 13 includes avariable AC power source having source impedance Rs, impedance matchingnetwork 24, selector 18, the upper AC to DC path including impedancematching network 12 and AC to DC converter 14, the lower AC to DC pathincluding impedance matching network 12 and AC to DC converter 14,combiner 20 and load 16 having variable load resistance R_(L). Theapparatus shown in FIG. 13 can convert AC power from the variable ACpower source to direct current to power load 16 with improved efficiencyover a wide range of input power and load resistance R_(L).

Variable AC power source can include an antenna, a piezoelectricelement, a generator, a vibration harvester, an acoustic harvester, or awind harvester. The source impedance R_(S) of the variable AC powersource is initially matched to the equivalent circuit of selector 18, ACto DC converters 14 and associated impedance matching networks 12,combiner 20, and variable load resistance R_(L) 16 using the secondimpedance matching network 24. The impedance matching networks 12 and 24can be, for example, Pi-, T-, L-, single-series element, or single-shuntelement impedance matching network that can contain combinations ofinductors and capacitors.

Selector 18 may be either active or passive. If the selector 18 isactive, a control unit can be used to select the appropriate path (i.e.,the upper AC to DC path or the lower AC to DC path) for the incomingsignal based on, for example, a power level or variable load resistanceR_(L) and the incoming signal can propagate along that path. If theselector 18 is passive, selector 18 can be implemented by, for example,a simple wired connection. In the passive case, the signal can besupplied to impedance matching network 12 of each of the upper AC to DCpath and the lower AC to DC path. The signal divides and most of thepower from the signal propagates along the path with the least mismatch(i.e., impedance mismatch) at the power level of the input signal.

AC to DC converters 14 can be, for example, a voltage doubler having oneor more stages, a charge pump, a series peak detector, a shunt peakdetector, a bridge rectifier, and/or other AC rectifying circuits. Eachof AC to DC converter 14 of the upper AC to DC path and AC to DCconverter 14 of the lower AC to DC path can be matched to apredetermined impedance value, such as 50 ohms, at different powerlevels using the respective impedance matching networks 12. That is, ACto DC converter 14 of the upper AC to DC path can be matched to animpedance value of 50 ohms at one power level using impedance network 12of the upper AC to DC path, and AC to DC converter 14 of the lower AC toDC path can be matched to an impedance value of 50 ohms at a differentpower level using impedance network 12 of the lower AC to DC path.

The DC output from AC to DC converter 14 of the upper AC to DC path isthen combined with the DC output from AC to DC converter 14 of the lowerAC to DC path using combiner 20. The DC combined output is sent tovariable load 16. Combiner 20 can be, for example, a simple hardwiredconnection such as a microstrip line, discrete components such asdiodes, or an active switching circuit such as a transistor, pindiode(s), or relay. Impedance matching network 24 can be included toprevent or mitigate interference between the upper AC to DC path and thelower AC to DC path. For example, use of a passive (e.g., a directlywired connection) selector at selector 18 and/or passive combiner atcombiner 20 can result in interference between the upper AC to DC pathand the lower AC to DC path.

The upper AC to DC path and the lower AC to DC path mitigate efficiencylosses by creating multiple AC to DC paths by use of multiple AC to DCconverters 14. The multiple AC to DC paths allow each path to beoptimized for a given characteristic (e.g., different input powerlevels, different impedances, and/or different load resistances) toprovide a near optimal performance over a wider range of inputparameters.

Additionally, AC to DC converters 14 can be adjusted or configured tohave different output resistances to mitigate output impedancemismatches between AC to DC converters 14 and load 16 to enable theapparatus to operate optimally at more than one output or loadresistance. The output resistance of AC to DC converters 14 can beadjusted to operate optimally at (i.e., have a matched impedance with)more than one output or load resistance by using different diodes,transistors, or other non-linear elements at AC to DC converters 14 ofthe upper AC to DC path and the lower AC to DC path, or by usingdifferent AC to DC topologies within the upper AC to DC path and thelower AC to DC path. In other words, the output resistances of the AC toDC converters 14 can vary with input power and/or variable loadresistance R_(L) to reduce impedance mismatches between AC to DCconverters 14 and load 16. Diodes having different parameters orcharacteristics such as different resistance, impedance, turn-onvoltage, junction capacitance, or other characteristic at AC to DCconverters 14 of the upper AC to DC path and the lower AC to DC path canbe used to vary the output resistances of the AC to DC converters 14.

The upper AC to DC path and the lower AC to DC path can be used togetherwith AC to DC converters adjustable to have different output resistancesto, for example, combine input impedance matching at different powerlevels with output impedance matching for improved AC to DC conversionefficiency. The result provides an AC to DC conversion efficiency graphwith two peaks (each corresponding to one of the upper AC to DC path andthe lower AC to DC path) unlike the single peak of the prior art shownin FIG. 3. The resulting graph has a nearly constant conversionefficiency over a wider range of load 16 resistances as shown in FIG.14.

Furthermore, the conversion efficiency is nearly constant over a widerrange of input power as shown in FIG. 17. In some embodiments, theapparatus shown in FIG. 13 is implemented as an RF power harvester.Because input power is dependent upon distance from a poweringtransmitter in such applications, the nearly constant conversionefficiency over a wider range of input power means that the apparatusconverts harvested power efficiently over a wider range of distancesfrom the powering transmitter.

The technique of multiple AC to DC paths matched at different inputpower levels with different output resistances works exceptionally wellwhen connecting the apparatus shown in FIG. 13 to a battery forrecharging purposes or to an LED for direct powering (e.g., load 16 isreplaced with a battery or LED). The battery or LED equivalentresistance is inversely proportional to the input power to the AC to DCconverter, which means at low power levels the battery or LED looks likea large resistor while at high power levels the battery or LED lookslike a small resistor. This realization allows each path to be optimizedfor a specific power level and load resistance at the battery or LED. Asan example, the upper AC to DC path in FIG. 13 could be impedancematched at a high power level and AC to DC converter 14 in that pathcould be designed to have a low optimal load resistance. The lower pathcould be impedance matched at a low power level and AC to DC converter14 in that path could be designed to have a high optimal loadresistance. The resulting converter using passive selector and passive(e.g., directly wired) combiner is shown in FIG. 15.

It will be understood by those skilled in the art that while theforegoing description sets forth in detail preferred embodiments of thepresent invention, modifications, additions, and changes might be madethereto without departing from the spirit and scope of the invention.

What is claimed is:
 1. An apparatus, comprising: a power sourceconfigured to produce a power; a first alternating current to directcurrent (AC-to-DC) converter operatively coupled to the power source andconfigured to receive a first portion of the power when the power iswithin a first power range, the first AC-to-DC converter configured tooutput a first direct current based on the power; and a second AC-to-DCconverter operatively coupled to the power source and configured toreceive a second portion of the power when the power is within a secondpower range different from the first power range, the second AC-to-DCconverter configured to output a second direct current based on thepower.
 2. The apparatus of claim 1, wherein the second AC-to-DCconverter is configured to receive a third portion of the power when thepower is within the first power range, the third portion of the powerbeing smaller than the second portion of the power.
 3. The apparatus ofclaim 1, wherein the power source is configured to produce an inputsignal having the power.
 4. The apparatus of claim 1, wherein the firstAC-to-DC converter has a first output resistance and the second AC-to-DCconverter has a second output resistance different from the first outputresistance.
 5. The apparatus of claim 1, wherein the power source is avariable AC power source.
 6. The apparatus of claim 1, wherein the powersource includes an antenna configured to wirelessly receiveradio-frequency (RF) energy.
 7. The apparatus of claim 1, furthercomprising an impedance matching network configured to match a sourceimpedance of the power source with the first AC-to-DC converter or thesecond AC-to-DC converter.
 8. The apparatus of claim 1, furthercomprising a selector operatively coupled to the first AC-to-DCconverter and the second AC-to-DC converter and configured to receivethe power, the selector configured to direct the first portion of thepower to the first AC-to-DC converter when the power is within the firstpower range, the selector configured to direct the second portion of thepower to the second AC-to-DC converter when the power is within thesecond power range.
 9. The apparatus of claim 8, wherein the selector ispassive.
 10. The apparatus of claim 1, wherein the first AC-to-DCconverter is operatively coupled to a load and configured to provide thefirst direct current to the load, the first output resistance beingsubstantially equal to a resistance of the load.
 11. An apparatus,comprising: a first impedance matching network and a first alternatingcurrent to direct current (AC-to-DC) converter defining a first powerpath optimized to receive a first portion of a power when the power iswithin a first power range; and a second impedance matching network anda second AC-to-DC converter defining a second power path optimized toreceive a second portion of the power when the power is within a secondpower range different from the first power range.
 12. The apparatus ofclaim 11, wherein the first power path is optimized to receive an inputsignal having the first portion of the power and the second power pathis optimized to receive the input signal having the second portion ofthe power.
 13. The apparatus of claim 11, wherein: the first impedancematching network is operatively coupled to a power source and the firstAC-to-DC converter, the power source configured to produce the power,the first impedance matching network configured to receive the firstportion of the power from the power source and to output the firstportion of the power to the first AC-to-DC converter when the power iswithin the first power range, the second impedance matching networkoperatively coupled to the power source and the second AC-to-DCconverter, the second impedance matching network configured to receivethe second portion of the power from the power source and to output thesecond portion of the power to the second AC-to-DC converter when thepower is within the second power range.
 14. The apparatus of claim 11,wherein the first power path is optimized for a first characteristic andthe second power path is optimized for a second characteristic differentfrom the first characteristic.
 15. The apparatus of claim 11, whereinthe first power path is optimized for a first input power and a firstload resistance, and the second power path is optimized for a secondinput power and a second load resistance.
 16. The apparatus of claim 11,wherein the first AC-to-DC converter has a first output resistance andthe second AC-to-DC converter has a second output resistance.
 17. Theapparatus of claim 11, wherein the first power range is lower than thesecond power range, the first power path having an optimal loadresistance higher than an optimal load resistance of the second powerpath.
 18. The apparatus of claim 11, wherein the first power path isoptimized to receive the first portion of the power having a powerwithin the first power range at a predetermined frequency and the secondpower path is optimized to receive the second portion of the powerhaving a power within the second power range at the predeterminedfrequency.
 19. An apparatus, comprising: a first alternating current todirect current (AC-to-DC) converter configured to receive a firstportion of a power when the power is within a first power range, thefirst AC-to-DC converter configured to output a first direct current; asecond AC-to-DC converter configured to receive a second portion of apower when the power is within a second power range different from thefirst power range, the second AC-to-DC converter configured to output asecond direct current; and a load operatively coupled to the secondAC-to-DC converter and configured to receive operational power from thesecond AC-to-DC converter based on the second direct current, the loadnot operatively coupled to the first AC-to-DC converter.
 20. Theapparatus of claim 19, wherein the power is a power of an input signal.21. The apparatus of claim 19, wherein the first AC-to-DC converter hasa first output resistance and the second AC-to-DC converter has a secondoutput resistance different than the first output resistance.
 22. Theapparatus of claim 20, wherein the load has a resistance substantiallyequal to the second output resistance.
 23. The apparatus of claim 19,wherein the load is a light emitting diode (LED) and the second powerrange is higher than the first power range.
 24. The apparatus of claim19, wherein the load is a microcontroller and the second power range ishigher than the first power range.
 25. The apparatus of claim 19,wherein the load includes a power storage device.
 26. The apparatus ofclaim 19, further comprising a direct current to direct current(DC-to-DC) converter operatively coupled to the second AC-to-DCconverter and configured to receive the second direct current andregulate a voltage level of the second direct current such that avoltage level of the operational power received by the load remainswithin a predetermined voltage range.
 27. The apparatus of claim 19,further comprising an antenna configured to wirelessly receiveradio-frequency (RF) energy and produce the power.